Zinc contamination

[slickinks]

Hello to all on the boards. I'm new to casting, but so far I've got around 25-30 pounds of wheel weights melted into ignots. I hear a lot about how zinc contamination can mess up the lead for filling out the mold, but how can I tell if this is happening when I pour my molds? Since I didn't have a thermometer when I melted the weights down into ignots, I'm concerned about it. Won't lead still run out over the sprue opening as gravity causes the mold to fill up regardless if there is zinc contamination? How does the mold 'not fill out' if there is zinc present in the alloy?

Thanks for all replies,

Slick

[Aegis]

The boolits look like they are wrinkled, like the mold or lead is to cool. Turned up the heat and they are still wrinkled. Usually the melt will change colors. I'm thinking it had a light blue tint.

[462]

First of all, you'd definitely know if, during the smelting process, you had any zinc contamination, as it turns the melt to an oatmeal consistancy.

One common example of poor mould fillout is ill-defined drive bands. Yes, the mould fills and runs over onto the top of the sprue cutter, but since the mould wasn't up to it's optimum casting temperature, the alloy cooled before it was able to completely fill the cavity. Wrinkled boolits is another symptom of a not-hot-enough mould.

Mould temperature is what it all about, not alloy temperature.

[slickinks]

First of all, you'd definitely know if, during the smelting process, you had any zinc contamination, as it turns the melt to an oatmeal consistancy.

One common example of poor mould fillout is ill-defined drive bands. Yes, the mould fills and runs over onto the top of the sprue cutter, but since the mould wasn't up to it's optimum casting temperature, the alloy cooled before it was able to completely fill the cavity. Wrinkled boolits is another symptom of a not-hot-enough mould.

Mould temperature is what it all about, not alloy temperature.

462,

That's the type of info that I was looking for: your reference to the contaminated melt being the consistency of oatmeal is a big help! And per both recommendations, I will definitely play close attention to mold temps when actively dropping boolits.

[captaint]

Now, lets everybody read 462's post again - and remember what it said. See there ?? It's easy !!!
enjoy Mike

[cbrick]

How does the mold 'not fill out' if there is zinc present in the alloy? Slick

Welcome to Castboolits Slick,

The answer to your question is "surface tension" of the alloy. With lead alloys you add tin for the purpose of reducing the surface tension of the molten alloy which allows the alloy to flow into all the little nooks & crannies in the mold giving good fill-out.

Even with tin in the alloy zinc will have a very tough surface tension and the boolits will be very poorly filled out. It's possible to cast decent boolits with zinc but it takes far more heat than normal casting temps. In addition tin looses it's ability to reduce surface tension much past 750 degrees.

When smelting WW alloy I am carefull to never let the pot get over 700 degrees which is well under the melting point of zinc, any zinc weights will float to the surface and I'll skim them off. In addition I snip any suspect weights with wire cutters, you'll know instantly if it's zinc so I have a far less chance of getting zinc in the melt in the first place.

Rick

[Harry O]

When I had zinc contamination, it did not get the the point where the mould did not fill out well. I had problems getting it to drain out the bottom pour spout. I opened up the spout with a wire several times, but it would drain fitfully and then stop again. Even with the mould going as hot as it would go, it was not hot enough to drain properly.

[fredj338]

Yeah, zinc can really screw up a melt. I had a friend send me some ingots, they had some zinc in them, I could tell when I dropped them into my pot. They melt at a higher temp & get a kind of oatmeal crud on top. Best advice, avoid it at all cost. I ended up having to drain the pot completely & start over, couldn't get the bottom pour to flow. In small amounts, like a few oz in 20#, maybe fine w/ constant fluxing, but drop 4# into a 30# pot, bad juju.

[I'll Make Mine]

If you have less than 2% zinc relative to your lead, you might not even know you have zinc in the melt; it'll stay in solution, even well below the melting point of unalloyed zinc, and simply act as a hardening additive. Go above that figure, and you start seeing the oatmeal (due to partial melting of a non-homogenous pot) as long as you're below the melting point of zinc.

[shadygrady]

if you got zinc send it to me

[Jim Flinchbaugh]

if you got zinc send it to me

I got a coffee can in the shed with your name on it, trouble is, I dont get that many zinc'ers in my ww's
When it fills up, I'll shout

[rintinglen]

I just finished up using the last of a pot of zinc contaminated wheel weights. I found that I could get decent boolits only if I cast hot and added 3 ingots of known clean metal to each one of the zinced ones. My clue was the quadrupling of my reject rate using known good molds.

[savage308]

I have a lot to learn about zinc

[Smoke4320]

Ok really dumb newbe question as said above "Cut with snips and you will know instantly " How will you know ?
is it harder, Smear instead of clean cut ? or what

Thanks

[cbrick]

You won't be able to even ding steel or zinc weights, lead ones will be easily cut into. You'll know instantly after you find a zinc weight what the difference is.

Rick

[Smoke4320]

Thanks for that .. never used WW's . until now just cast pure lead for Blackpowder
Just tryed Pure lead powdercoated 458 socom bullets Traveling at approx 1650 FPS .. 6 shots and no leading

so next going to add approx 2% tin and shoot 15 to 20 bullets ..

again thanks for the explaination

looking to learn all I can about making alloys and sources for lead

[BubbaJon]

462,

That's the type of info that I was looking for: your reference to the contaminated melt being the consistency of oatmeal is a big help! And per both recommendations, I will definitely play close attention to mold temps when actively dropping boolits.
It was my experience that this was the look around 600-650F. At 720 it did NOT look like that but I had the wrinkly boolits and poor fillout. One of the knowlegeable members here - 44 man I think - clued me to bringing the heat up slowly to 600 and fluxing with sawdust. If you have zinc you'll see it as that stuff clumps in the flux.
Scoop it until smooth and don't look back. BTW - there's an excellent thread here on hand sorting weights that can save you a a LOT of grief before it happens. I did my weights before i knew what teh hell I was doing and the zinc weights got trapped and melted before they floated to the top. I also wished I'd washed them first as dirt and sand was a secondary issue. I now have 80 lbs of good alloy but I would have been toast without the awesome advice on here.

[Charlie U.]

If you get too much zinc in your pot is it better to add pure lead to dilute it down or can the zinc be separated and drossed off?
Will fluxing the melt help separate the zinc?

[BubbaJon]

If you get too much zinc in your pot is it better to add pure lead to dilute it down or can the zinc be separated and drossed off?
Will fluxing the melt help separate the zinc?
Read my post again - flux with pine sawdust around 600F and that stuff will clump around the flux and you just scoop it out. I got the guys in the lab here at the university to do an electron scanning analysis and I had almost 3% zinc in the dross I scooped off. After this fluxing (several times I might add) I had none left in my alloy. It works.

[colonelhogan44]

I have also read you can get it out with sulfur...just make sure it's far away from air that you breathe.

[GT1]

Good to read, I bought some muffins last year that I'm pretty sure have some zinc in them. I was going to try adding pure lead into it until I had usable results, but I'd rather try fluxing with sawdust to get it workable.